1. Field of the Invention
The present invention relates to an image processing apparatus and an image processing method, and particularly an image processing apparatus and an image processing method capable of extracting feature amount data to be used in face authentication.
2. Description of the Related Art
A face verification apparatus has conventionally been known to execute authentication processing based on image data obtained by photographing a human face. The face verification apparatus receives input of a face image of a person to be authenticated, which is photographed by an imaging apparatus using a solid image sensor. The face verification apparatus acquires feature amount data of the person to be authenticated, which indicates a feature amount of components constituting the face such as eyes, a nose, a mouth and a face contour, from a face image. Then, the face verification apparatus checks the feature amount data of a registered person stored in advance with each feature amount data of the person to be authenticated. The face verification apparatus determines similarity of the person to be authenticated with the registered person. Then, the face verification apparatus authenticates the person to be authenticated as the registered person who is determined to have the maximum similarity.
When the maximum similarity is smaller than a predetermined authentication threshold value, it is determined that the person to be authenticated is an unregistered person (the person to be authenticated is not verified as the registered person). Further, when the maximum similarity is equal to the authentication threshold value, it is previously determined that the person to be authenticated will be verified as either a registered person or an unregistered person.
The face verification apparatus supplies a result of authentication, for example, to a control apparatus for locking/unlocking a door of facilities. The control apparatus locks/unlocks the door according to the result of authentication. Further, it is discussed to utilize the face verification apparatus for specifying a user who makes a transaction at an automated teller machine (ATM). More specifically, it is discussed to install an imaging apparatus in an ATM to identify a user using a face image of the user photographed by the imaging apparatus. Accordingly, an operation such as insertion of a card (for example, a cash card) and entering of a personal identification number which has been used for authentication of a user becomes unnecessary, which improves operability.
A conventional face verification apparatus stores feature amount data of a registered person that is obtained from a front face image of the registered person. On the other hand, a lighting condition (lighting direction, brightness, color of lighting) in which the face image of a person to be authenticated is photographed during verification is determined depending on an installation environment of an imaging apparatus and a posture of the person to be authenticated during imaging processing. Thus, depending on the installation environment of the imaging apparatus, similarity between the feature amount data acquired from the face image of the person to be authenticated and the feature amount data of the registered person which corresponds to the person to be authenticated may be decreased. As a result, even when the person to be authenticated is the registered person, the person may be misidentified as an unregistered person.
In order to reduce probability of occurrence of misidentification (that is, a false rejection rate) which verifies a person to be authenticated who is a registered person as an unregistered person, an authentication threshold value may be set low. On the contrary, when the authentication threshold value is set low, the probability of occurrence of misidentification (that is, a false acceptance rate) is increased, which verifies a person to be authenticated who is not a registered person as the registered person. Thus, a security level is decreased. Accordingly, the authentication threshold value is set corresponding to the security level which is required in a system to be applied to the face verification apparatus. More specifically, in a system which requires a high security level, the authentication threshold value is set high. Thus, a reduction in a false acceptance rate is prioritized over a reduction in a false rejection rate.
Japanese Patent Application Laid-Open No. 2005-56004 discusses a technique for storing feature amount data of a registered person that is obtained from a plurality of face images photographed under different lighting conditions. This technique can improve authentication accuracy by reducing both the false rejection rate and the false acceptance rate. More specifically, the face images of the registered person are made into a three-dimensional (3D) model image. A plurality of two-dimensional (2D) model images different in lighting condition is generated from the 3D model image. Then, the feature amount data of the registered person is acquired from the plurality of the generated 2D model images and stored.
However, in a configuration discussed in Japanese Patent Application Laid-Open No. 2005-56004, since a plurality of pieces of the feature amount data of the registered person which is obtained from the plurality of face images in different lighting conditions needs to be stored for one registered person, there is a problem that registration operation is extremely troublesome. Then, there is a similar problem when not only the feature amount data of the registered person is stored but also the feature amount data of a person to be authenticated for determining similarity with the feature amount data of the registered person is acquired. More specifically, there is a problem in that the feature amount data of the person to be authenticated needs to be acquired from a plurality of face images which are photographed while changing the lighting conditions, in order to eliminate an influence of the lighting condition.